The genius of social media is that they propagated some labels and then they let people do the hard work of adjusting their personalities and belief systems to more closely adhere to those labels. Likely driven by mimetic desire for status and recognition. Adherence to well known labels provides instant recognition and validation.
Then when it came to 'targeted advertising', social media advertisers could just target the labels and reach a huge amount of people because those people had already fine-tuned and optimized themselves to be receptive to that kind of messaging.
Their personalities were homogenized to the point that the focus groups ended up being representative of the real people behind the labels.